Organic Chemistry : Help with Aldol Condensation

Study concepts, example questions & explanations for Organic Chemistry

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Example Questions

Example Question #1 : Help With Aldol Condensation

Screen shot 2015 07 07 at 8.30.46 pm

Determine the major product of the given intramolecular aldol reaction.

Screen shot 2015 07 07 at 8.30.53 pm

Possible Answers:

None of these

II

III

IV

I

Correct answer:

II

Explanation:

Keep in mind the following principles: Cyclization is favored when a five/six-member ring may be formed. Addition at an aldehyde is favored relative to the same reaction at a ketone. 

As a result, abstraction of a hydrogen bound to carbon 6 (an alpha-carbon) is favored since the resulting carbanion may attack the aldehyde (carbon 1) to form a six-member ring, resulting in compound II. Compound I results from abstracting a hydrogen from carbon 2, generating a carbanion which may then attack the ketone. Based on the latter of the above principles, this is a minor product.

Example Question #2 : Help With Aldol Condensation

What is the final organic product of the reaction shown?

Screen shot 2015 11 13 at 2.54.29 pm

Screen shot 2015 11 13 at 2.54.56 pm

Possible Answers:

III

IV

I

II

V

Correct answer:

I

Explanation:

First step: Friedel-Crafts acylation of benzene

Second step: Formation of enolate

Third step: aldol addition (enolate attacks carbonyl carbon in benzaldehyde)

Fourth step: neutralization of anion and dehydration forming alkene

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